metamorphic
Schist (Oxidized)
Mica Schist with Iron Oxide staining
Hardness: 3.5-4 Mohs (mica components) to 6-7 (quartz components); Color: Grey base with reddish-brown, orange, and tan iron oxide patinas; Luster: Silky to sub-metallic; Structure: Foliated with visible medium-to-large grained flaky minerals; Cleavage: Excellent basal cleavage in mica layers; Density: 2.5-2.9 g/cm³.
- Hardness
- 3
- Luster
- Silky to sub-metallic
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Physical properties
Hardness: 3.5-4 Mohs (mica components) to 6-7 (quartz components); Color: Grey base with reddish-brown, orange, and tan iron oxide patinas; Luster: Silky to sub-metallic; Structure: Foliated with visible medium-to-large grained flaky minerals; Cleavage: Excellent basal cleavage in mica layers; Density: 2.5-2.9 g/cm³.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high grades of pressure and temperature. The varied colors seen here are the result of secondary chemical weathering (oxidation) of iron-bearing minerals like biotite or pyrite within the rock.
Uses & applications
Commonly used as a decorative stone in landscaping, for flagstones, and occasionally as a source for industrial mica. It is not suitable for heavy construction due to its tendency to flake along foliation planes.
Geological facts
The word schist is derived from the Greek word 'schizein' meaning 'to split,' referring to the ease with which the rock can be divided into thin layers. The presence of garnet crystals is very common in this rock type, though none are prominently visible on this weathered surface.
Field identification & locations
Identify in the field by looking for 'schistosity'—a preferred orientation of platy minerals that gives the rock a sparkly or platy appearance. It is abundant in mountain ranges and metamorphic belts worldwide, such as the Appalachians or the Alps.
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